In recent years high quality color printers have become widely available. Two significant and related factors are improvements in color accuracy and improvements in resolution. For inkjet printers, typical resolutions are 1200 pixels per inch or higher, which translates into a printer ink dot size (and separation) of 20 microns or less. In many systems the inkjet printer may overprint regions multiple times to reduce the effect of printer defects, such as blocked printer head nozzles. The optical density of a printed color can be very sensitive to the precise value of the displacement between overprinted regions. This means that (for high quality printers at least) it is necessary to control or calibrate the exact shift of the printer head relative to the printed medium between overprints. Typically, the desired accuracy of this calibration is on the order of one micron.
Many approaches have been proposed for calibrating the movements of the medium being printed relative to the head size on the medium (where, as depicted in FIG. 4, the physical distance 420 on a print medium 230 between two ink dots 410 is referred to as the “head size” 420), but few prior art methods measure the effective head size as printed on the medium.
One possible method to measure the effective head size on the medium is by printing dots using predefined nozzles and then measuring the separation of the dots on the medium using a microscope. However, because printed dots on the medium could have a dimension of around 40 micrometers (because the printed dots may have irregular shapes), and because microscopes with the desired accuracy are typically very expensive, such measurements are not always practical.
Noting that high quality colour printers have become a norm, it is further noted that two significant and related factors in such printers are improvements in colour accuracy and improvements in resolution. For inkjet printers, typical resolutions are 1200 dpi or higher, which translates into a printer ink dot size (and separation) of 20 microns or less. In many systems, the inkjet printer may overprint regions multiple times to reduce the effect of printer defects, such as blocked printer head nozzles. The optical density of a printed colour can be very sensitive to the precise value of the displacement between overprinted regions. This means that (for high quality printers at least) the exact shift of the printer head relative to the printed medium between overprints must be controlled or calibrated. Typically, the desired accuracy of this calibration is on the order of one micron.
A number of techniques have been proposed for calibrating the movements of the medium being printed relative to the head size on the medium, but few techniques measure the effective head size as printed on the medium.
One method of measuring the effective head size on the medium is to print dots using predefined nozzles and then measuring the separation of the dots on the medium using a microscope. However, because printed dots on the medium could have a dimension of around 40 micrometers and may have irregular shapes, and because microscopes with the desired accuracy are typically very expensive, such measurements are not always practical.